Optimism is targeting 200 ms subblocks on OP Mainnet, cutting the preconfirmation interval from 250 milliseconds with a gradual rollout planned for August 31. Four fields in the streamed payload will return zero values: state_root, block_hash, and withdrawals_root will be all-zero, while withdrawals will be an empty list. This silent change creates a compatibility risk because the payload type remains ExecutionPayloadFlashblockDeltaV1, preventing software from detecting the anomaly. Direct WebSocket stream consumers and RPC providers must audit their systems before these zero values reach downstream applications. Alchemy and QuickNode have already updated their documentation to reflect the migration.
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